Malignant Glomus Tumour (Glomangiosarcoma) with Additional Neuroendocrine Differentiation in a Horse.

A 13-year-old Icelandic crossbred horse was presented with headshaking and progressive impairment of chewing. A slowly growing mass was identified in the anterior maxilla. This was associated with lysis of the alveolar bone and the roots of the incisors and there were nodular proliferations affecting the nasal septum and conchae. There was no response to chemotherapy and so the horse was humanely destroyed. Based on morphological, immunohistochemical and ultrastructural findings the mass was classified as a malignant glomus tumour with multifocal vascular spaces and additional neuroendocrine differentiation. An oronasal glomus tumour with neuroendocrine differentiation has not been described previously in an animal.